PROJECT SUMMARY/ABSTRACT A large body of research has elucidated the role of bleach (HOCl) as a potent antimicrobial produced by the immune system through neutrophil myeloperoxidase, but new findings have provided intriguing instances in which this paradigm is challenged, and some important human bacterial pathogens such as Salmonella Typhimurium and Helicobacter pylori have been shown to actually be attracted to inflamed tissue?where HOCl can reach millimolar concentrations?and can exploit host inflammation processes to colonize and establish persistent infections. The molecular basis for how these bacteria can use motility and chemotaxis to respond to HOCl and reaction products is mostly unknown, and represents an important new direction for infectious disease research with the potential to provide many insights into how pathogenic and commensal bacteria colonize and persist in animal hosts to cause disease. The broad and long-term objective of this project is to learn how host-associated bacteria navigate the inflammation and redox landscape of the gut, which has implications for many human infectious diseases, especially those involving bacterial-promoted chronic inflammation such as stomach cancer, ulcerative colitis, and inflammatory bowel diseases. The key focus of this project is to advance understanding of how host-associated bacteria sense and respond to inflammation by investigating a novel bleach-sensing regulatory module referred to as chemoreceptor zinc-binding (CZB) domains that are conserved broadly in commensal and pathogenic bacteria. Specific Aim 1 will use a reductionist in vitro approach to test if CZB domains function through a conserved mechanism by analyzing residue conformation patterns and determining the reactivity with HOCl of representative CZB proteins from H. pylori, S. Typhimurium, and E. coli. Specific Aim 2 will perform the first tests of the biological roles of CZB domains in bacterial infections with a novel ELISA chemotaxis assay and infections in zebrafish and mouse model organisms. Important for the Career Development of Dr. Arden Perkins, this project will provide him comprehensive new training in using animal models, which he has never done, as well as expertise in microscopy and live imaging, and genetic engineering of bacteria. This training will build on Dr. Perkins? prior experience in protein crystallography, drug discovery, and redox biology to make him a competent investigator at the interface of in vitro and in vivo work, and enable him to pursue investigations into the functions of key proteins involved in bacterial infections at the molecular and biological levels. Dr. Perkins will be trained at University of Oregon in the zebrafish system, a high throughput model in which he will study bacterial dynamics and responses to neutrophils in situ, and collaborators Dr. Manuel Amieva at Stanford and Dr. Andreas Baumler at UC Davis will provide expert guidance and support for extending these studies to mouse models of infection of H. pylori and S. Typhimurium, respectively.